The present invention relates to a circuit for regulating the torque of ratio meters in general. In particular the invention relates to a circuit for regulating the torque of ratio meters, particularly of compass indicators, in which oil branches (1 and 2) are connected to respective two-quadrant voltage-controlled sources of current (4, 6) which are fed via (voltage) amplifiers (3, 5) with a sine signal voltage and cosine signal voltage, respectively
In general, ratio meters operate in the manner that the deflection of the pointer is dependent on the ratio of the currents flowing through two coil branches of the ratio meter. Thus, in first approximation, the absolute values of the currents do not affect the deflection of the pointer as long as their ratio remains the same. This basic advantage of the ratio meter is, however, limited by the fact that, in the case of small currents in the coil branches, the torque produced is not sufficient to definitely move the pointer into the exact position corresponding to the currents. If (measurement) amplifiers are used to amplify weak currents, the control limits of the amplifier, on the other hand, must be observed, since otherwise, if the input voltage of the amplifiers exceeds a predetermined value, then the output voltage is no longer proportional. These limits of accuracy of the measurement principle of a ratio meter are even narrower in actual practice, due to manufacturing tolerances. These limits of accuracy are disturbingly noticeable in the case of a measurement in which the position of the horizontal component of the terrestrial magnetic field with respect to the longitudinal axis of a vehicle is to be measured and converted into a proportional deflection of the pointer of a ratio meter. The horizontal component of the induction is greatly dependent on the geographical position of the vehicle.
Specifically, in one known compass system having a magnet probe which operates in accordance with the known principle of the flux-gate magnetic-field measurement a sine signal voltage and a cosine signal voltage are produced which correspond to the sine and cosine respectively of the angle of a vector of the horizontal component of induction of the magnetic field surrounding the magnet probe, referred to a given axis (the longitudinal axis of the vehicle). The sine signal voltage and the cosine signal voltage are converted, in each case via a voltage-controlled source of current which operates in two characteristic-curve quadrants, into proportional currents each of which is fed into a separate one of the two coil halves of the ratio meter. The deflection of the pointer of this ratio meter is then proportional to the arc tangent of the ratio of the two signal voltages. As stated above, however, this compass system can operate satisfactorily only in certain geographical locations. For this reason, upon the manufacture of the compass system at least one part, namely the magnet probe, is so adapted that the signal voltages lie in a predetermined range at the intended place of use. This procedure results in greater expense in connection with manufacture and stocking.
In highly developed compass systems which permit compensation for the magnetic declination and the deviation produced by the vehicle, an analog computer is used to process the sine signal voltage and the cosine signal voltage, the amount of the vector, among other things, being formed in it from the two signal voltage components. This so-called b-signal is used to form the sine and the cosine of the vector direction of the horizontal component of the induction with respect to the given axis. It has not been attempted to use this b-signal, which also represents a measure of the amount of the horizontal component of the induction, for the amplitude standardization of magnetic fields of different intensity by dividing the sine and cosine signal voltages by the amount of the vector. This use would also be limited to said high-grade compass systems in which the b-signal is calculated in a relatively expensive manner.
The object of the present invention is to create a circuit for the less expensive regulating of the torque of ratio meters in which each coil half is traversed by a current which is produced from an amplified signal voltage by a voltage-controlled source of current operating in two quadrants. This circuit, therefore, makes it possible to dispense with an analog computer for the division by the so-called b-signal.